Design of optimum interpolation filters for digital demodulators

Interpolation filtering in digital demodulators with fixed input sampling rate is treated. The procedures for optimum interpolation filter design which account for the peculiarities of the digital demodulators are presented. Minimum mean square error (MMSE) interpolation filters are discussed, and a design procedure for standard input signals is given. For some hardwired implementations the on-line computation of the filter coefficients can be advantageous. For those cases, the MMSE approach is almost infeasible and polynomial approximations are used. New design algorithms for coefficient computation for optimum polynomial interpolators are given. The design procedure is illustrated by a number of examples, and the results are compared to the nonpolynomial MMSE case.